Technical Field
An aspect of the present invention relates to a friction material composition, a friction material using the friction material composition, and a production method thereof.
Background Art
A friction material to be used for a disc brake, a drum brake, etc. is composed of a fiber base material for imparting a reinforcing action, a friction adjusting material for imparting a friction action and adjusting its friction performance, and a binder for binding these components. These constituents are appropriately adjusted according to the intended use, the required performance, etc.
For example, JP-A-10-139894 discloses that, in a non-asbestos friction material for brakes, which uses a thermosetting resin as a binder component and contains a fiber base material, a filler and an additive, a porous spherical particle formed by binding of crystal grains of titanic acid compounds as a friction adjusting material is added. According to this technique, the fade resistance can be improved without impairing the strength or wear resistance of the friction material. In JP-A-10-139894, the titanium acid compound to be added as a friction adjusting material is produced by preparing a granulated powder through wet mixing and spray drying of raw materials and firing it.
In a friction material for brakes, the porosity of the friction material is generally adjusted to a range of approximately from 10 to 30% for enhancing the fade resistance or high speed effectiveness. Therefore, in the case of passing a puddle in rain, washing a car or parking a vehicle outdoors during the night, the friction material comes into a moisture-absorbed state. In such a moisture-absorbed state, when the vehicle speed is reduced to generally 5 km/h or less, i.e. just before stop by braking, or when a brake is completely released after loosening the brake at the time of starting an automatic car, a low-frequency abnormal noise attributable to a creep torque is generated. This low-frequency abnormal noise is also called creep noise and accompanied by discomfort and therefore, reduction thereof is demanded.
In order to solve such a problem, JP-A-2000-191800 discloses that a fluorine-based polymer having water repellency is blended with a friction material including a fiber base material, a friction adjusting material, a lubricant, and a binder. In such a friction material, the fluorine-based polymer having water repellency is scattered in a conventional matrix having hydrophilicity and therefore, even when the friction material is caused to absorb a large amount of water by car washing, etc., the creep noise can be reduced.
However, it has been reported that even by the technique described in this document, when the friction material is in a moisture-absorbed state after braking under a light load, creep noise is generated. Therefore, development of a friction material further improved in the properties preventing creep noise generation (noise characteristics) is demanded.
Patent Document 1: JP-A-10-139894
Patent Document 2: JP-A-2000-191800